U.S. Pat. No. 3,426,238 discloses the concept of nondestructively reading out stored information from the storage target of a direct-viewing bistable storage tube wherein the reading electron beam is pulsed as it is raster scanned across the storage target.
Reading out stored and nonstored information that is displayed on the storage target of a direct-viewing bistable storage tube is known by the teaching of U.S. Pat. No. 3,600,509.
Making a permanent or hard copy of information displayed on the storage target of a direct-viewing bistable storage tube is covered in U.S. Pat. No. 3,679,824.
These direct-viewing bistable storage tubes have been made larger so that more information can be stored and visibly displayed on the large storage targets thereof, especially for computer use. Reading out this stored information from these large storage targets in accordance with the teachings of the above-identified patents is necessary in order to make permanent copies of the stored and/or nonstored information.
The electrical readout signals that have been obtained from the corners of the large storage targets have been poor in relation to the readout signals that have been obtained from other areas of the storage targets. It has been found that this is due to the lack of sufficient flood electrons in the corner areas, because, when flood guns were positioned at the corners of the storage target, the amplitude of the readout signals from the unwritten areas in the target coorners was substantially less than the amplitude of the readout signals from the unwritten areas in the target corners when no flood guns were positioned thereat.